German patent specification DE 260030 discloses a so-called double-girder gantry crane having two horizontal crane girders and two vertical support girders which form a gantry frame of the gantry crane. The crane girders extend in parallel and at a spaced interval with respect to each other. Arranged at each of the lower ends of the support girders is a travelling mechanism, by means of which the gantry crane can be moved in a direction of travel extending transversely with respect to the longitudinal direction of the crane girders. A crane trolley having a cable winch can be moved on and along the crane girders. According to the design as a double-girder crane, a load picking-up means of the cable winch arranged on the crane trolley is lowered or raised between the two crane girders. The crane girders are designed as trussed girders and comprise in each case an upper run and a lower run, which are each oriented horizontally and in parallel with each other, and vertically extending, rod-shaped posts and diagonally extending, rod-shaped struts which connect the upper and lower runs.
German utility model document DE 1 971 794 U describes a further double-girder overhead crane whose horizontal crane girders are designed in a similar manner as trussed girders and comprise in each case plate-shaped upper runs, rod-shaped lower runs and rod-shaped posts. A rail for a crane trolley is attached to each of the upper runs in the region of their inner edges.
German patent specification DE 37 31 245 C2 discloses a crane girder, designed as a box girder, for a double-girder overhead crane. The box girder includes an upper run and a lower run which are connected together via two side walls. The upper run is formed by a rolled profile designed as a T-profile girder having a horizontal flange and a vertical web which protrudes inwardly into the box girder and forms a reinforcing rib for the flange. Centrally and above the web, a rail which extends in the longitudinal direction, has a rectangular cross-section and consists of a solid material is welded onto the flange of the T-profile girder.
German utility model document DE 66 04 483 U discloses a double-girder overhead crane having two crane girders designed as box girders. The box girders are each composed of two I-girders. For this purpose, upper and lower flanges of the I-girders are connected together in that a multiplicity of run plates are arranged at a spaced disposition with respect to each other, are distributed over the entire length of the girders and are welded to the upper or lower flanges. Instead of a multiplicity of run plates, a single-piece, continuous upper run plate can be used for the upper flanges.
German laid-open document DE 22 39 573 A discloses a trussed girder. An upper run of the trussed girder is composed of two U-profiles, in that the mutually facing webs thereof are screwed together. In this respect, posts and struts of the trussed girder are arranged with their upper ends between the two webs of the U-profiles and are fixedly clamped via the screw connection.